1. Field of the Invention
The present invention relates to semiconductor processing technology and, in particular, concerns a chemical mechanical polishing system which incorporates a chemical mechanical polishing pad, such as a fixed abrasive chemical mechanical pad, having hydrophilic surfaces for enhanced wetting of the semiconductor substrate during the chemical mechanical polishing process.
2. Description of the Related Art
Chemical mechanical polishing or planarization (CMP) is a technique whereby surfaces, such as semiconductor substrates, are planarized by the simultaneous application of both an etching and a polishing process. CMP is typically used to globally planarize surfaces such as the upper surface of a semiconductor wafer. The wafer is typically positioned within a carriage and is rotated with respect to a polishing pad. In one approach, a slurry containing abrasive particles and an etchant is interposed between the polishing pad and the surface of the semiconductor wafer that is to be planarized. The polishing pad is then brought into contact with the surface of the wafer that is to be planarized and the combination of the mechanical polishing and the etchant results in the exposed surfaces of the wafer being removed by the CMP process.
CMP is particularly well-suited for global planarization of wafers having many semiconductor structures, such as DRAM memories, formed thereon. By planarizing the wafer during the fabrication of the semiconductor devices, additional layers can be deposited onto the wafer while utilizing less surface area of the wafer. This allows for the formation of higher density devices and devices that are structurally stronger.
One difficulty that occurs in typical CMP processes is that the abrasive contained within the slurry often flocculates when the slurry is mixed with particular chemicals added to the slurry to enhance particular CMP parameters. The flocculation of the abrasive particles results in a localized increase in concentration of the abrasive particles on particular surface regions of the semiconductor wafer with respect to other regions of the semiconductor wafer. This can result in uneven planarization of the semiconductor wafer and possibly even result in scratching of the wafer and damage to the devices and structures formed on the semiconductor wafer. Moreover, mixing the abrasive particles into the slurry so as to obtain a uniform distribution of the abrasive particles in the slurry during the CMP process can be very complicated and difficult. In particular, premixed abrasive particles may separate prior to introduction to the interface between the polishing pad and the semiconductor wafer or the slurry may clog various jets and orifices in the CMP system resulting in localized differences in the density of the abrasive within the slurry and wafer planarization.
These types of problems have led to the development of CMP systems wherein the abrasive is not encapsulated within the slurry but is actually part of the polishing pad. One such fixed abrasive polishing pad is disclosed in U.S. Pat. No. 5,879,222 which discloses a particular type of polishing pad having abrasive particles captured within the polishing pad. In fixed abrasive polishing pads, the abrasive is encapsulated in the pad and is preferably uniformly distributed over the pad so that the wafer is in contact with a more uniform quantity of abrasive particles during the CMP process. The slurry thus does not contain the abrasive particles and, therefore, uniformity of distribution of the abrasive particles over the surface of the wafer during the CMP process is improved. While currently available fixed abrasive polishing pads solve some of the problems associated with abrasive laden slurry-based CMP processes, many fixed abrasive polishing pads inhibit wetting of the semiconductor substrate that is to be polished.
In particular, it is desirable that there be a sufficient quantity of liquid, such as water, on the surface of a semiconductor wafer that is to be chemically mechanically polished so as to enhance the polishing process. The liquid serves as a lubricant and inhibits the abrasive particles from gouging into the surface being planarized. In the absence of such liquid, abrasives, either from a fixed abrasive polishing pad or abrasive contained within a slurry, can generate localized scratches on the surface of the semiconductor wafer which can result in damage to devices formed on this surface. Further, the absence of the liquid may also result in excessive heat on the surface being planarized causing additional damage to this surface.
One factor which contributes to these problems is that the polishing pads used either for fixed abrasive polishing pads or for standard slurry-based polishing pads are often formed of hydrophobic materials, such as urethane-based materials. Consequently, the water contained within the slurry mixture is not attracted to the portion of the polishing pad that is actually polishing the semiconductor wafer. This results in a potential reduction of wetting of the semiconductor wafer at the point of contact between the polishing pad and the semiconductor wafer. This problem is particularly acute with fixed abrasive polishing pads wherein the fixed abrasive is often captured within a hydrophobic resin such that water is not attracted to the polishing interface.
It will be appreciated that the problem of localized damage or scratching to semiconductor surfaces becomes a much greater problem as the scale of integration of the integrated circuits formed on the semiconductor wafer increases. As the scale of integration increases, the devices are formed much smaller such that a small scratch may damage one or more devices. In very large scale or ultra large scale applications, even very small scratches in the semiconductor surface can result in damage to the underlying devices. As a consequence, the hydrophobic nature of many prior art CMP polishing pads, including both slurry-type pads and fixed abrasive pads, that inhibit wetting at the polishing interface, can significantly affect yield during device formation.
Hence, there is a need for a chemical mechanical polishing pad that is adapted to reduce damage to the semiconductor wafer as a result of reduced wetting at the interface between the polishing pad and the surface of the semiconductor wafer being polished. To this end, there is a need for a CMP pad, which can either be a fixed abrasive pad or a slurry-based polishing pad, that provides for greater wetting of the surface at the interface between the pad and the surface being planarized.
The aforementioned needs are satisfied by the CMP member of the present invention which is comprised of a substrate and a plurality of polishing protrusions extending from a first surface of the substrate. The plurality of polishing protrusions are adapted to polish and remove an exposed surface of a semiconductor wafer during a CMP process. The first surface of the substrate is hydrophilic so as to retain wetting fluid adjacent the protrusion such that the wetting fluid is retained at the interface between the polishing protrusions and the semiconductor wafer.
In one aspect of the invention, a CMP polishing member is provided which is comprised of a substrate having a plurality of protrusions extending from the substrate wherein the plurality of protrusions contain a fixed abrasive that is encapsulated therein. The first surface of the substrate includes a hydrophilic material so as to attract and retain water adjacent the fixed abrasive protrusions during the polishing process to thereby enhance wetting of the semiconductor surface during a CMP process. In one embodiment, the protrusions are comprised of a plurality of discrete protrusions positioned about the polishing member. In another embodiment, the protrusions are comprised of a plurality of spiral wedges separated by grooves wherein the hydrophilic material is positioned within the grooves.
In another aspect of the invention, a CMP polishing pad having a substrate and a plurality of fixed abrasive protrusions is provided. The fixed abrasive protrusions and the polishing pad are coated with a hydrophilic material that is removed from a distal portion of the fixed abrasive protrusions so as to expose the fixed abrasive to a surface of a semiconductor wafer that is to be chemically mechanically planarized. The hydrophilic coating is adapted to retain wetting fluid adjacent the exposed fixed abrasive surface of the protrusions to thereby enhance wetting of the semiconductor surface during the CMP process.
It will be appreciated that the CMP polishing member of the present invention enhances wetting of the semiconductor surface during the CMP process in both fixed abrasive CMP pad systems and slurry-based nonabrasive CMP pad systems. These and other objects and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings.